Sony FX 6 Quick Start Manual page 46

Custom Shooting Mode: Project Settings
Once the Menu/User/Base Setting/Target Display is set to SDR(BT.709) setting,
Custom mode will appear as Custom (709) in the status pages.
On status page 4, you can also change the Shooting Mode. This is the project page.
Look at the other selections on this page: 4K UHD at 23.98p using the full sensor of
the camera and the best internal codec (XAVC I). See next page for details.